Method and apparatus for c-v2x radio resource allocation

ABSTRACT

Methods and apparatuses for allocating cellular vehicle-to-everything (C-V2X) radio transmission resources for transmitting messages in a C-V2X network from amongst a pool of initial resources comprised within a plurality of subframes are disclosed. For each subframe in the plurality of subframes, it is determined whether transmitting in the subframe is likely to cause reception degradation with other C-V2X messages being transmitted in the network, and if yes, all resources in the subframe are excluded prior to allocating a resource for transmission.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/726,606 filed Dec. 24, 2019 (now allowed) and is related to andclaims the priority benefit of U.S. provisional patent application Ser.No. 62/787,331 filed Jan. 1, 2019.

FIELD

Embodiments disclosed herein relate generally to efficient C-V2Xresource allocation, and more specifically to methods forself-allocating resource blocks in a manner that reduces the likelihoodof transmission conflicts between vehicles that are likely to causereception degradation.

BACKGROUND

The term “cellular vehicle-to-everything” or C-V2X refers to vehicularconnectivity specifications defined by 3GPP (3rd Generation PartnershipProject) using the LTE sidelink PC5 interface to support direct linkcommunication between vehicles without involving a cellularbase-station. A given LTE physical channel is divided into smallerfragments, both in time and frequency, which are referred to as“frames”. A frame consists of 10 subframes in the time domain. Eachsubframe is 1 ms wide and contains two time-slots. In the frequencydomain, a LTE frame is divided into 12 subcarriers, separated from eachother by 15 kHz. The subcarriers are further divided into resourceblocks (RB). Each radio resource consists of one subframe (1 ms) in timeand a number of RBs in frequency. Several resources can occupy a singlesubframe. Devices that utilize a sidelink PC5 interface must reserve or“allocate” a resource for transmission. After a reservation or “latency”period, the same resource is used again for the next transmission. Thispattern is repeated for a few seconds, after which a new resource isallocated.

Mode 4 of the LTE sidelink PC5 interface as defined by 3GPP Release 14requires that a transmitting device autonomously allocate a resourcefrom amongst a pool of potential resources. Thus the sidelink PC5 (Mode4) allocation scheme as applied to C-V2X involves the C-V2X devicelistening to the communication channel and keeping a record of allreceived signals from other vehicles over the last 1 second (1000subframes). This record is utilized to make intelligent resourceselection decisions by excluding resources deemed too busy. A resourceis then selected from amongst the non-excluded resources using arandomly selected counter. Release 15 of 3GPP follows the same resourceallocation scheme. Release 16 is likely to follow the same scheme aswell, renaming it as Mode 2.

It is important to note that while a single subframe includes multipleresources, an inherent limitation exists in the LTE sidelink PC5 in thata device transmitting in a subframe is disabled from receivingtransmissions in that same subframe. Moreover, if several devicestransmit in the same subframe, a receiving device within range of thetransmitting devices might not be able to receive all of thetransmissions, as the dynamic range of the receiving device's radiotransceiver is not capable of coping with both the strongest and weakestsignals.

As a result of the above limitations, the resource selection decision isan important one. Poor resource selection will limit the communicationrange of the transmission (e.g. if another vehicle transmits in theselected resource with a stronger signal), while a good selectiondecision will choose the resource with minimal interference to othervehicles. However, the existing scheme often results in a poor selectiondecision, because resources are probed individually without consideringthe utilization, or lack thereof, of other resources in the samesubframe.

Thus, there remains a need for, and it would be advantageous to have, amore efficient allocation scheme which makes allocation decisions thatconsider the utilization of other resources in the same subframe.

SUMMARY

In various embodiments, there are provided, in a C-V2X communicationunit for transmitting messages in a C-V2X network, methods forallocating radio transmission resources from amongst a pool of initialresources, the pool of resources comprised within a plurality ofsubframes, a method comprising determining, for each subframe in theplurality of subframes, whether transmitting in the subframe is likelyto cause reception degradation with other C-V2X messages beingtransmitted in the network, and if yes, excluding all resources in thesubframe prior to allocating a resource for transmission.

In various embodiments, there is provided a C-V2X communication unit fortransmitting messages in a C-V2X network, the C-V2X communication unitconfigured to allocate radio transmission resources from amongst a poolof initial resources, the pool of resources comprised within a pluralityof subframes, the C-V2X communication unit comprising a processorconfigured to determine, for each subframe in the plurality ofsubframes, whether transmitting in the subframe is likely to causereception degradation with other C-V2X messages being transmitted in thenetwork, and if yes, exclude all resources in the subframe prior toallocating a resource for transmission.

In some embodiments, the determining whether transmitting in thesubframe is likely to cause reception degradation and if yes, excludingall resources in the subframe includes: a) setting an initialhalf-duplex (“HD”) energy threshold; b) for each subframe in theplurality of subframes, excluding all resources within the subframe ifat least one resource within the subframe has energy above the HD energythreshold; c) after the exclusion if the number of remaining resourcesis not greater than a predetermined percentage of initial resources,increasing the HD energy threshold; and d) repeating steps b) through c)until the number of remaining resources is greater than thepredetermined percentage of initial resources.

In some embodiments, in step a) the initial HD threshold is set tobetween −70 dBm and −80 dBm, and in step b) the HD threshold isincreased by between 3 dBm and 5 dBm.

In some embodiments, determining whether transmitting in the subframe islikely to cause reception degradation and if yes, excluding allresources in the subframe includes: a) setting an initial near-far(“NF”) energy threshold; b) for each subframe in the plurality ofsubframes, excluding all resources within the subframe if at least oneresource within the subframe that is allocated has energy below the NFenergy threshold; c) after the exclusion if the number of remainingresources is not greater than a predetermined percentage of initialresources, decreasing the NF energy threshold; and d) repeating steps b)through c) until the number of remaining resources is greater than thepredetermined percentage of initial resources.

In some embodiments, in step a) the initial NF threshold is set tobetween −70 dBm and −80 dBm, and in step b) the NF threshold isdecreased by between 3 dBm and 5 dBm.

In some embodiments, the NF threshold is dependent on a Channel BusyRatio (CBR) of the network.

In some embodiments, after excluding resources, an average energy foreach remaining resource over a prior n subframes is determined, whereinthe number of subframes n differs for each remaining resource.

In some embodiments, the average energy for a given remaining resourceis determined by detecting whether a significant allocation change eventoccurred for the given resource; if yes, averaging the energy of theresource beginning from a time of detected significant allocation changeto present time; and otherwise, averaging the energy of the resourceover the last 1 second.

In some embodiments, a significant allocation change event for aresource includes at least one of, between two consecutive subframescomprising the resource, an allocation status of the resource beingflipped, and a difference in energy of the resource being greater than apredetermined threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments are herein described, by way of example only,with reference to the accompanying drawings, wherein:

FIG. 1 shows schematically an embodiment of a method of allocating C-V2Xradio resources according to known art;

FIG. 2 demonstrates graphically a known half-duplex problem and near-farproblem;

FIG. 3A shows schematically a high level flowchart of an embodiment of amethod of allocating C-V2X radio resources accordingly to the presentlydisclosed subject matter;

FIG. 3B shows more details of various steps in the method of embodimentof FIG. 3A;

FIG. 4 shows schematically an embodiment of a method of computing amodified energy value for resources in S_(A) accordingly to thepresently disclosed subject matter;

FIG. 5 shows schematically consecutive subframes containing a resourceR; and

FIG. 6 shows a block diagram of an embodiment of a system for allocatingC-V2X radio resources accordingly to the presently disclosed subjectmatter.

DETAILED DESCRIPTION

Standard methods of allocating a C-V2X radio resource in Mode 4 of LTEsidelink PC5 involve narrowing down the pool of potential resources to ashortlist S_(A) of available resources. The shortlist of availableresources is further narrowed down to an even shorter list S_(B) ofcandidate resources. A resource is then selected randomly from amongstthe candidate resources. The process is iterative, in that if S_(A)contains too few resources, S_(A) is discarded and the entire process ofnarrowing down resources repeats using more relaxed exclusionarycriteria until a satisfactory number of resources remain in S_(A).

FIG. 1 shows schematically the method for allocating C-V2X radioresources according to existing (known) art. Operation begins at step100 by initializing various parameters for excluding resources, such asthe SCI (Service Channel Indication) energy threshold. At step 102, theshortlist of resources S_(A) is cleared. At step 104, resources occupiedby SCI data and having SCI energy above the SCI energy threshold areexcluded. The remaining resources are added to S_(A). At step 106, adetermination is made as to whether shortlist S_(A) contains more than20% of the initial resources. If No (i.e. 80% or more of all initialresources were excluded), at step 108 the SCI energy threshold isincreased by 3 dB, and execution reverts back to step 102 whereshortlist S_(A) is cleared. Operation then continues at step 104, whereresources are excluded whose energy now exceeds the higher SCI energythreshold. This iterative process continues until shortlist S_(A)contains more than 20% of the initial resources. If yes in step 106, theprocess continues to step 110, where the resources in S_(A) are sortedaccording to their respective energy levels, averaged over the last 1second, and the weakest 20% are added to shorter list S_(B) of candidateresources. The sorting is performed according to resources' RSSI(Received Signal Strength Indication) value, linearly averaged over thelast 1 second. At step 112, a resource from amongst the candidateresources is selected randomly.

As explained next, this known art resource allocation scheme suffersfrom various drawbacks.

Changed Resource Allocation During the Last Second

At step 110 of the existing method, an average RSSI value is computedfor each resource in S_(B) using an averaging period of 1 second.However, the allocation state of any given resource may have changedduring the last second. By averaging over a relatively large period of 1second (1000 subframes), the current (known) scheme fails to consider aresource's allocation state change within the last second. Considerthree cases:

In a first case, if during the last 1 second a resource was initiallyallocated by a close vehicle (high energy) but then became unallocated(no energy), after averaging the resource will appear as having someenergy, thereby obscuring the resource's current state of beingunallocated.

Conversely, in a second case, if during the last 1 second a resource wasunallocated (no energy) and then became allocated by a close vehicle(high energy), after averaging the resource will appear to have lowenergy. This resource may still be considered for selection under thecurrent scheme even though it should in fact be excluded because of itscurrent high energy value.

Finally, in a third case, if during the last 1 second a resource hadweak energy for most of the initial portion of the last second but thenchanged to strong energy towards the tail end, after averaging theresource will appear to have a weak signal. In reality though, theresource should be excluded since the current high energy is likely tocause collisions.

“Half-Duplex” and “Near-Far” Problems

A further drawback with the current resource allocation scheme is basedon the inherent limitation described above whereby a vehicle cannotreceive transmissions in the subframe in which the vehicle istransmitting. This limitation gives rise to the well-known “half-duplex”problem, where two vehicles each transmit in different resources in thesame subframe. Another limitation in C-V2X message transmission arisesin which a strong signal, which may be received from a near vehicle, maydrown out a weaker signal, e.g. from a vehicle further away. This hasbecome known as the “near-far” problem.

FIG. 2 demonstrates graphically the half-duplex problem and near-farproblem.

Four vehicles 202, 204, 206 and 208 are concurrently transmitting C-V2Xmessages. The transmissions are labelled TX-1 212, TX-2 214, TX-3 216and TX-4 218, respectively. Vehicles 202 and 204 each transmit insubframe 222, so these vehicles will not receive each other's messageseven though they are close to one another. This is due to thehalf-duplex problem which arose when they each randomly selected thesame subframe. Vehicles 206 and 208 each transmit in the next subframe226, so vehicles 206 and 208 will also not receive each other'smessages.

Further with reference to FIG. 2, vehicle 206 and vehicle 208 transmitusing different resources in the same subframe. In this case, vehicle202, which is closer to vehicle 206 than to vehicle 206, will receivethe messages transmitted by vehicle 206 but not the messages transmittedby vehicle 208 due to the stronger signal of TX-3 216 transmitted byvehicle 206. In some cases, this situation may be tolerable or evenunavoidable, however ideally it is preferable to be able to receive bothmessages. Thus, the current PC5 scheme suffers from the additionaldrawback that in a non-congested network, no attempt is made to mitigatethe problems described above by giving preference to allocatingresources in vacant subframes.

Having described the existing drawbacks, various embodiments disclosedherein provide a method, executed by a C-V2X communication unittransmitting in a C-V2X network, of allocating C-V2X radio resourcesefficiently so as to minimize conflicts between resources in the samesubframe that are likely to cause reception degradation with other C-V2Xtransmissions in the network. As used herein, “reception degradation”should be understood to include reception that is affected byhalf-duplex problems and/or near-far problems. The method considers i)the likelihood of a resource, if utilized, to cause half-duplexproblems, ii) the likelihood of a resource, if utilized, to causenear-far problems, and iii) any significant allocation change eventswithin the last 1 second, as will be explained below.

FIGS. 3A-3B show schematically an exemplary embodiment of a method for,in a C-V2X communication unit for transmitting messages in a C-V2Xnetwork, allocating radio transmission resources from amongst a pool ofinitial resources, the pool of resources comprised within a plurality ofsubframes. Referring now to FIG. 3A, which shows a high-level flowchart,the method takes as input 301 each subframe in the plurality ofsubframes. At step 303, the method includes determining, for eachsubframe, whether transmitting in the subframe is likely to causereception degradation with other C-V2X messages being transmitted in thenetwork. If yes, at step 305 resources in the subframe are excluded fromallocation. If no, at step 307 resources in the subframe are notexcluded from allocation.

FIG. 3B shows more details of steps 303-307 of FIG. 3A. At step 300,three parameters are initialized: an SCI energy threshold, a half-duplex(HD) threshold and a near-far (NF) threshold. Initializing the SCIinitial energy is known in the art (step 100 of FIG. 1). In alternativeembodiments, only two thresholds may be initialized, e.g. the SCI energythreshold and the HD threshold, or the SCI energy threshold and the NFthreshold. The HD threshold and NF threshold are used to excluderesources with potential half-duplex problems and near-far problems,respectively. The initial HD threshold may be set to a relatively lowenergy value, for example about −70 dBm to about −80 dBm. The initial NFthreshold may be set to an energy value of about −70 dBm to about −80dBm.

In some embodiments, the value of the NF threshold may depend on thenetwork's channel busy ratio (CBR), with the underlying rationale beingthat in congested networks, i.e. networks with high CBR, near-farproblems cannot be avoided anyway, so excluding resources on such basiswould be too limiting. As an example of the dependency on CBR, in anetwork with a CBR of 15%, the NF threshold may be decreased by 15, e.g.from −80 dBm to −95 dBm. In a network with a CBR of 25%, the NFthreshold may be decreased by 25, e.g. from −80 dBm to −105 dBm.

Steps 302-304 are also similar to steps in known art (steps 102-104 ofFIG. 1,). At step 302, the shortlist S_(A) of available resources iscleared, and at step 304, resources that are occupied by SCI (ServiceChannel Indication) data and having energy above the SCI energythreshold are excluded. Steps 306-308 show further details of steps303-307 of FIG. 3A. At step 306, and in contrast with known methods,resources that pose a potential to a half-duplex problem are excluded.The available resources (i.e. those not excluded in step 304) in eachsubframe may be grouped according to their respective subframe. For eachgiven subframe, the energy of each resource within the given subframe iscompared with the HD threshold. If the energy of at least one resourcein the subframe is greater than the HD threshold, all of the resourcesin the given subframe are excluded. The energy of a resource may bedetermined by computing the average RSSI value for the resource in thegiven subframe.

At step 308 and in contrast with known methods, resources that pose apotential NF problem are excluded. An energy value (e.g. RSSI) iscomputed for each remaining resource (i.e. those resources not excludedin either of steps 304 or 306). The energy value is compared with the NFthreshold. As detailed above, in some embodiments, the NF threshold maybe a function of the network's CBR. Each resource's energy value iscompared with the NF threshold. If within any given subframe, aresource's energy value is lower than the NF threshold but is allocated(i.e. has SCI energy), all of the resources in the given subframe areexcluded. Non-excluded resources are then added to the shortlist S_(A).

At step 310, it is determined whether the number of resources in S_(A)is more than a predetermined percentage of the number of all initialresources, e.g. 20%. If not, too many resources were excluded in steps304-308. At this point, the exclusionary criteria are relaxed. At step312, the NF threshold is decreased, preferably by between about 3 dBmand 5 dBm. At step 314, the HD threshold is increased, preferably bybetween about 3 dBm and 5 dBm. At step 316, the SCI energy threshold isincreased by 3 dB as in the known art (step 108 of FIG. 1). Executionthen reverts back to step 302, where the shortlist S_(A) is cleared, andsteps 304-308 are repeated using the new thresholds. This iterativeprocess continues until at step 310 it is determined that the shortlistS_(A) contains more than 20% of the initial resources, at which pointexecution continues at step 318.

At step 318, a modified average energy value is computed for eachresource in S_(A). The modified average energy considers significantallocation change events, as will be detailed below with reference toFIG. 4.

At step 320, the resources in S_(A) are sorted according to theirrespective modified average energy values as computed in step 318, andthe lowest (i.e. weakest energy) 20% are selected as candidate resourcesS_(B). At step 322, a resource from amongst the candidate resources inS_(B) is selected randomly.

FIG. 4 shows schematically an embodiment of a method of computing amodified average energy value that considers significant allocationchange events. The method may be performed by the MAC (Media AccessControl) layer interface. As used herein, “significant allocation event”refers to a flipped allocation status (allocated to unallocated or viceversa), or to an energy level gain or drop between subsequent subframesin an amount greater than a predetermined threshold Th. The n^(th)subframe is denoted sf(n). Only subframes in the last 1 second thatcontain resource R are considered. Subframes are numbered in reversechronological order such that sf(1) represents the most recent subframecontaining resource R, and sf(2) represents the subframe containing Rthat is just prior to sf(1), as shown in FIG. 5.

At step 400, parameters are initialized by setting n=1. At step 402, theenergy E of resource R in the n^(th) subframe, denoted E(R_(sf(n))), isdetermined. At step 404, the value determined in step 402 is comparedwith the energy E of resource R in the (n+1)^(th) subframe, denotedE(R_(sf(n+1))). At step 406, it is determined whether the allocationstatus flipped, meaning either the resource was allocated in sf(n) (i.e.E(R_(sf(n)))≠0) and not allocated in sf(n+1) (i.e. E(R_(sf(n+1)))=0) orvice versa. The allocation state of a resource can alternatively bedetermined by examining the SCI energy level. If at step 406 it isdetermined that the allocation status flipped, execution continues atstep 414, where the average RSSI is computed for resource R between themost recent subframe and subframe sf(n). Otherwise, execution continuesto step 408, where it is determined whether the difference in energy ofresource

R between subframes sf(n) and sf(n+1) is greater than a predeterminedthreshold Th. Suitable values for Th can be, for example, any valuebetween 10-20 dB. If the difference in energy is greater than Th,execution continues at step 414, where the average RSSI is computed forresource R between the most recent subframe and subframe S(n).Otherwise, execution continues at step 410 where it is determinedwhether sf(n+1) is the last (i.e. oldest) subframe containing resourceR. If Yes, execution continues at step 416 where the average RSSI iscomputed for resource R across all subframes. Otherwise, executioncontinues at step 412 where n is increased by one (1) and steps 402-410are repeated until either a significant allocation change has beendetected (steps 406 or 408 evaluate to true), or all subframes have beenexamined (step 410 evaluates to true).

FIG. 6 shows a block diagram of an embodiment of a system 600 forallocating C-V2X radio resources. System 600 includes a C-V2Xcommunication unit 602 configured to transmit and receive C-V2Xmessages, including configuration for performing related activitynecessary for transmitting and receiving C-V2X messages. C-V2Xcommunication unit 602 includes a processor 604, a non-volatile memory(NVM) 606, a radio transceiver 608, and a PHY (Physical) Layer 612 alloperatively coupled with one another. PHY Layer 612 is configured tosend and receive radio signals to/from radio transceiver 608 and toperform PHY transport layer functions, including sensing resource energylevels and providing sensing reports to the processor. Processor 604includes an enhanced MAC layer 610 configured to perform MAC layertransport functions including allocating C-V2X radio resources fortransmitting C-V2X messages according to the methods described herein.In some embodiments, the enhanced MAC Layer 610 can alternatively resideoutside of processor 604 and be operatively coupled to processor 604 oreven comprise its own processor. In operation, the enhanced MAC layer610 requests a sensing report from the PHY layer 612, and the PHY Layer612 returns the requested report. The sensing report contains the energyvalues of all resources in the last 1 second (1000 subframes). Thesevalues may be stored in NVM 606. Using the sensing report, the enhancedMAC layer 610 executes steps 303-307 of FIG. 3A and steps 300-322 ofFIG. 3B in order to allocate C-V2X resources according to the methoddescribed herein.

It should be noted that the method described above and in FIGS. 3A-3Bshould be understood to include (i) embodiments in which resources areexcluded only on the basis of potential HD problems only (steps 306 and314 of FIG. 3B), (ii) embodiments in which resources are excluded onlyon the basis of potential NF problems (steps 308 and 312 of FIG. 3B),(iii) embodiments in which a modified average energy value is calculatedfor resources in S_(A) (step 318 of FIG. 3B) without excluding resourcesfor potential HD problems or potential NF problems, and (iv) embodimentsthat include any combination of (i), (ii) and (iii).

While this disclosure has been described in terms of certain embodimentsand generally associated methods, alterations and permutations of theembodiments and methods will be apparent to those skilled in the art.The disclosure is to be understood as not limited by the specificembodiments described herein, but only by the scope of the appendedclaims.

What is claimed is:
 1. A method, comprising: in a cellularvehicle-to-everything (C-V2X) network: receiving a subframe thatincludes a plurality of resource blocks; determining whethertransmitting in a resource block of the subframe is likely to causereception degradation for C-V2X messages being transmitted in otherresource blocks of the subframe; and, if yes excluding all resourceblocks in the subframe from allocation for transmission.
 2. The methodof claim 1, further comprising: after excluding all resource blocks,determining an average energy for each remaining resource block over anumber n of prior subframes, wherein the number of subframes n differsfor each remaining resource block.
 3. The method of claim 1, wherein thedetermining whether transmitting in a resource block of the subframe islikely to cause reception degradation for other C-V2X messages beingtransmitted in other resource blocks of the subframe and, if yesexcluding all resource blocks in the subframe from allocation fortransmission comprises: i) setting an initial half-duplex (“HD”) energythreshold, ii) for each subframe in the plurality of subframes,excluding all resource blocks within the subframe if at least oneresource block within the subframe has energy above the HD energythreshold, iii) after the exclusion, if the number of remaining resourceblocks is not greater than a predetermined percentage of initialresource blocks, increasing the HD energy threshold, and iv) repeatingsteps ii and iii until the number of remaining resource blocks isgreater than the predetermined percentage of initial resource blocks. 4.The method of claim 3, wherein the initial HD threshold is set tobetween −70 dBm and −80 dBm, and wherein the HD threshold in ii isincreased by between 3 dBm and 5 dBm.
 5. The method of claim 2, whereinthe average energy for a given remaining resource block is determined bydetecting whether a significant allocation change event occurred for thegiven remaining resource block, and if yes, averaging the energy of thegiven remaining resource block beginning from a time of detectedsignificant allocation change to a present time.
 6. The method of claim5, wherein if the detecting whether a significant allocation changeevent occurred for the given remaining resource block indicates that asignificant allocation change event did not occur, the method furthercomprises averaging the energy of the given remaining resource blockover the last 1 second.
 7. A cellular vehicle-to-everything (C-V2X)communication unit for transmitting messages in a C-V2X network,comprising: a processor configured to receive a subframe that includes aplurality of resource blocks, to determine whether transmitting in aresource block of the subframe is likely to cause reception degradationfor C-V2X messages being transmitted in other resource blocks of thesubframe, and, if yes, to exclude all resource blocks in the subframefrom allocation for transmission.
 8. The C-V2X communication unit ofclaim 7, wherein the processor is further configured, after excludingall resource blocks, to determine an average energy for each remainingresource block over a number n of prior subframes, wherein the number ofsubframes n differs for each remaining resource block.
 9. The C-V2Xcommunication unit of claim 7, wherein the processor configurationfurther includes a configuration to: i) set an initial half-duplex(“HD”) energy threshold, ii) for each subframe in the plurality ofsubframes, exclude all resource blocks within the subframe if at leastone resource block within the subframe has energy above the HD energythreshold, iii) after the exclusion, if the number of remaining resourceblocks is not greater than a predetermined percentage of initialresource blocks, increase the HD energy threshold, and iv) repeatingsteps ii and iii until the number of remaining resource blocks isgreater than the predetermined percentage of initial resource blocks.10. The C-V2X communication unit of claim 9, wherein the initial HDthreshold is set to between −70 dBm and −80 dBm, and wherein the HDthreshold in ii is increased by between 3 dBm and 5 dBm.
 11. The C-V2Xcommunication unit of claim 8, wherein the processor is configured todetermine the average energy for a given remaining resource block bydetecting whether a significant allocation change event occurred for thegiven remaining resource block, and if yes, averaging the energy of thegiven remaining resource block beginning from a time of detectedsignificant allocation change to a present time.
 12. The C-V2Xcommunication unit of claim 11, wherein if the detecting whether asignificant allocation change event occurred for the given remainingresource block indicates that a significant allocation change event didnot occur, the processor is further configured to average the energy ofthe given remaining resource block over the last 1 second.